This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-247914, filed Sep. 1, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a voice coil motor control apparatus which is designed for use in a disk drive in which the head actuator driven by a voice coil motor moves a head in a radial direction of a disk, and which supplies an electric current to the voice coil motor to control the voice coil motor.
A hard disk drive incorporates a hard disk, a magnetic head, a rotary actuator, and a voice coil motor (VCM). The head records data on the hard disk. The head is mounted on the actuator. The voice coil motor drives the actuator. When driven, the actuator moves the head in the radial direction of the hard disk until the head reaches a target position (i.e., a target track). Moving the head to the target position is known as xe2x80x9cseek operation.xe2x80x9d Positioning the head at a position in the target track is known as xe2x80x9ctrack following operationxe2x80x9d or xe2x80x9cpositioning operation.xe2x80x9d
FIG. 5 shows the major components of the conventional VCM control circuit incorporated in a disk drive. As shown in FIG. 5, the VCM comprises a VCM drive circuit 101. The VCM drive circuit 101 has a switch that comprises four FETs (Field Effect Transistors) 101A to 101D. The FETs 101A to 101D are connected, forming an H-type bridge. The FETs 101A to 101D are turned on or off in accordance with switch control signals (i.e., gate control signals) G1 to G4. Each FET can control an electric current by virtue of on-resistance. The node 102 of the FETs 101A and 101C is connected to the power supply circuit 110 of the disk drive. The node 103 of the FETs 101B and 101D is connected to the ground. The power supply circuit 110 usually applies a voltage to the VCM drive circuit 101. This voltage is of the same level as the power-supply voltage applied from a host system (e.g., a personal computer). A series circuit is provided between and connected to the node of the FETs 101A and 101B and the node of the FETs 101C and 101D. The series circuit comprises the coil (VCM coil) 131 and sense resistor 132 of a VCM 130. The VCM 130 is incorporated in a head actuator.
To supply a current to the VCM coil 131 to make the VCM 130 generate a drive force, the FETs 101A and 101D are turned on, while the FETs 101B and 101C are turned off, thereby supplying a current in the direction of arrow A. To supply a current in the opposite direction of arrow B, the FETs 101A and 101D are turned off and the FETs 101B and 101C are turned on.
The current flowing in the VCM coil 131 (i.e., VCM current) has a value (I) which is determined as follows:
I=(VPxe2x88x92VB)/(RC+RS+RF)
where VP is the output voltage of the power supply circuit 110, VB is the back electromotive force of the VCM 130, RC is the resistance of the VCM coil 131, RS is the resistance of the sense resistor 132, and RF is the sum of the on-resistances of two FETs.
The value (I) of the VCM current determines the speed of the head actuator. That is, the value (I) determines the speed at which the head moves in the disk drive.
The direction in which the VCM current flows determines the direction in which the actuator moves. It ultimately determines the direction in which the head moves (toward the innermost track or toward the outermost track.) Hence, the direction and speed in and at which the head moves can be controlled by changing the direction in which the VCM current flows and the magnitude of the current.
The VCM current can be detected by measuring the voltage generated across the sense resistor 132. Hence, the speed of the head can be controlled by changing the on-resistance of each FET in accordance with the voltage across the sense resistor 132, or the VCM current determined by the voltage. The on-resistance of each FET is determined by the gate voltage of the FET. The gate voltage is, in-turn, determined by the output (DAC) of a digital/analog converter, which corresponds to the control value corresponding to a target VCM current.
As indicated above, the conventional VCM control circuit uses the power supply of the disk drive. In other words, the power supply of the host system is used as the VCM voltage source in the conventional VCM control circuit. As pointed out above, the value (I) of the VCM current is determined by four factors, that is, the power-supply voltage, the resistance of VCM coil 131, the resistance of sense resistor 132, and the on-resistance of each FET. Note that the power-supply voltage, the resistance of VCM coil 131 and the resistance of sense resistor 132 are constant at a specific temperature. The VCM current is therefore controlled by changing the on-resistances of two FETs remain on. The VCM current is maximal when the output (DAC) of the digital/analog convertor represents a control value that minimizes the on-resistance of each FET.
In most cases, the maximum current is made to flow in the VCM coil 131 during the seek operation, wherein the head moves for a long distance. In the seek operation, the head moves over the disk, from the innermost track to the outermost track, or vice versa.
In the host system, the power-supply voltage may be switched to a low voltage to save electric power, in the low power-consumption mode. In this case, the output voltage of the power supply circuit 110 (i.e., the power-supply voltage for the VCM) is switched to a low voltage in the disk drive, too. As a result, the maximum current supplied to the VCM 130 decreases Inevitably, the maximum torque the VCM 130 generates will be smaller, reducing the highest speed of the head. The power can indeed be saved, but the seek operation is impaired in terms of efficiency.
To enhance the operating efficiency of a disk drive, the disk must be accessed at high speed. The disk-accessing speed depends on the seek-operation speed. It is therefore demanded that the seek operation be performed at high speed. To shorten the seek-operation time, the torque of the VCM must be increased. However, the power-supply voltage the conventional VCM control circuit can supply to the VCM depends on the power-supply voltage applied from the host system. Inevitably, the largest current that can be supplied to the VCM is limited.
In the conventional VCM control circuit for use in a disk drive, the maximum current applied to the VCM cannot be increased above the rated value in order to increase the torque of the VCM. Hence, it is impossible to increase the seek-operation speed, or shorten the seek-operation time, thereby to enhance the operating efficiency of the disk drive. Further, maximum current supplied to the VCM decreases when the power-supply voltage applied to the VCM control circuit is switched to a low voltage because the host system is set into the low power-consumption mode. In this case, too, the torque of the VCM decreases, lowering the seek-operation speed. This will prolong the seek operation.
An object of this invention is to provide a voice coil motor control system that increases the power-supply voltage applied to a disk drive, thereby increasing the maximum current supplied to the VCM provided in the drive, moving the head at higher speed and, ultimately, shortening the seek-operation time.
Another object of the invention is to provide a voice coil motor control system that increases the power-supply voltage applied to a disk drive when this power-supply voltage applied is switched to a low voltage, thereby preventing the maximum current supplied to the VCM from decreasing to lower the speed at which the head moves or to prolong the seek operation.
A voice coil motor control according to this invention is designed to control the voice coil motor for driving a head actuator provided in a disk drive. The apparatus comprises: a power supply circuit for receiving power from an external apparatus and outputting a prescribed power-supply voltage for driving the voice coil motor; a voltage step-up circuit for increasing the power-supply voltage output from the power supply circuit, thereby to output an increased voltage; voltage control means for selecting one of the increased voltage and the power-supply voltage under predetermined conditions; drive current generating means for generating a drive current in accordance with the voltage selected by the voltage control means; and a motor drive controller for supplying a drive current to the voice coil motor to drive the voice coil motor.
The voltage step-up circuit increases the power-supply voltage applied from the host system to the disk drive, and the voltage increased is used as the power-supply voltage of the voice coil motor (VCM). The maximum current that can flow in the VCM is thereby increased. The power-supply voltage for the VCM can be raised in the disk drive even if the power-supply voltage applied to the disk drive falls when the host system is set into a power-saving mode. The VCM can therefore keep generating the rated torque, moving the head at the prescribed seek-operation speed. As long as the power-supply voltage applied to the disk drive remains at a prescribed voltage, the seek-operation time can be shortened. This helps to enhance the performance of the disk drive.
Preferably, the voltage step-up circuit is a charging-pump type that has a capacitor. The charging-pump type circuit is small, making it possible to render the disk drive more compact than in the case where the voltage step-up circuit is of any other type.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.